1. Field of the Invention
This invention relates generally to devices for delivering anesthetic gas or gases in medical applications. More particularly, it relates to a novel respiratory gas delivery system of the “demand” or “self-administered” type adapted to be used with a disposable breathing and scavenging circuit.
2. Brief Description of the Related Art
The incorporated applications disclose novel respiratory face mask and breathing circuit assemblies adapted to be used with commercially available anesthetic gas handling equipment commonly and heretofore used in dentistry. Such anesthetic gas usually includes a mixture of nitrous oxide and oxygen. When employed as intended, the respiratory face mask and breathing circuit assemblies of the incorporated applications avoid contaminating the surrounding environment with built-up waste N2O gas, thereby facilitating safe and effective combined use of such equipment for sedation purposes in a hospital or other clinical environment as distinguished from a dentist's office.
U.S. Pat. No. 4,527,558 to Hoenig discloses a system for delivering anesthetic gas to a patient from a gas mixing device through a combined breathing mask and a demand valve assembly. A demand valve is normally closed to the flow of gas therethrough, but is responsive to the vacuum caused by a patient breathing through the mask attached to the valve, to allow the passage of gas through the valve and mask assembly until the patient ceases to inhale, or begins to exhale.
When the patient exhales, the demand valve has already shut off the supply of anesthetic gas until the next inspiration cycle. In the '558 patented system, the combined mask and demand valve assembly (i.e. both units) is located remotely and distally at the end of a flexible supply hose or tube which, in turn, is connected to the gas mixing device. This enables the patient to hold the demand valve and mask assembly by hand and self-administer the aesthetic gas (e.g. typically a mixture of N2O and oxygen). In the system of the '558 patent, a separate flexible tube attached to the output of the demand valve is connected to a surge tank or chamber for storing exhaled gas so as to ostensibly help prevent the exhaled gas from contaminating the room environment. The surge tank, in turn, is connected to a central vacuum system for scavenging the exhaled waste gas stored in the surge tank.
The disclosure of U.S. Pat. No. 4,527,558 is hereby incorporated hereinto and made part of this application by reference.
The foregoing anesthetic gas delivery and scavenging system according to the '558 patent has several disadvantages. Because the demand valve and mask assembly is held by the patient, and the patient breathes through the demand valve and scavenging (exhalation) tubing and surge tank, these fixed non-disposable components of the system must be cleaned or sterilized after each patient use to avoid cross-contamination (i.e. only the face mask or insert is disposable). Additionally, because the patient must manually grasp the relatively bulky mask and demand valve assembly during gas administration, the demand valve, a relatively delicate mechanism, is susceptible of being damaged by being dropped or otherwise mishandled by the patient. Moreover, the scavenger or surge tank is of fixed volume and can be overwhelmed by vigorous exhalation causing venting and possible room contamination. Also, the surge tank tends to collect moisture which compromises its function and tends to promote growth of bacteria or other contagions. Finally, the surge tank includes a hydrophobic polyurethane resistance plug which may increase the difficulty of exhalation experienced by the patient.
However, in view of the art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the field of this invention how the shortcomings of the prior art could be overcome.